What is hail?

Hail is produced when supercooled water drops circle around in a zone with upward streaming of a Cumulonimbus cloud.
While the water drops circle through zones with different temperatures and humidity, they grow by accumulating layers of ice.

The hailstone freezes and melts when it moves through cold and warm air.
The clouds reach a height of 10,000 to 15,000 meters at a temperature of -50°C. The higher this cloud belt the bigger the hailstone will be.
This hail is formed during a summer thunderstorm and cannot be compared to winter hail, which is actually supercooled rain (frozen raindrops).
Often this precipitates under the form of dust hail.

In the case of thunderstorm there is a large potential difference between the earth and the cloud, which gives rise to a lightning bolt (discharge).
In the case of winter hail there is no notable potential difference.